/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.phoenix.iterate;

import java.sql.SQLException;
import java.util.Collections;
import java.util.List;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.phoenix.compile.ExplainPlanAttributes;
import org.apache.phoenix.compile.ExplainPlanAttributes.ExplainPlanAttributesBuilder;
import org.apache.phoenix.compile.QueryPlan;
import org.apache.phoenix.compile.StatementContext;
import org.apache.phoenix.monitoring.OverAllQueryMetrics;
import org.apache.phoenix.monitoring.ReadMetricQueue;
import org.apache.phoenix.query.KeyRange;
import org.apache.phoenix.util.ClientUtil;

import org.apache.phoenix.thirdparty.com.google.common.collect.Lists;

/**
 * Create a union ResultIterators
 */
public class UnionResultIterators implements ResultIterators {
  private final List<KeyRange> splits;
  private final List<List<Scan>> scans;
  private final List<PeekingResultIterator> iterators;
  private final List<ReadMetricQueue> readMetricsList;
  private final List<OverAllQueryMetrics> overAllQueryMetricsList;
  private boolean closed;
  private final StatementContext parentStmtCtx;

  public UnionResultIterators(List<QueryPlan> plans, StatementContext parentStmtCtx)
    throws SQLException {
    this.parentStmtCtx = parentStmtCtx;
    int nPlans = plans.size();
    iterators = Lists.newArrayListWithExpectedSize(nPlans);
    splits = Lists.newArrayListWithExpectedSize(nPlans * 30);
    scans = Lists.newArrayListWithExpectedSize(nPlans * 10);
    readMetricsList = Lists.newArrayListWithCapacity(nPlans);
    overAllQueryMetricsList = Lists.newArrayListWithCapacity(nPlans);
    for (QueryPlan plan : plans) {
      readMetricsList.add(plan.getContext().getReadMetricsQueue());
      overAllQueryMetricsList.add(plan.getContext().getOverallQueryMetrics());
      iterators.add(LookAheadResultIterator.wrap(plan.iterator()));
      splits.addAll(plan.getSplits());
      scans.addAll(plan.getScans());
    }
  }

  @Override
  public List<KeyRange> getSplits() {
    if (splits == null) return Collections.emptyList();
    else return splits;
  }

  @Override
  public void close() throws SQLException {
    if (!closed) {
      closed = true;
      SQLException toThrow = null;
      try {
        if (iterators != null) {
          for (int index = 0; index < iterators.size(); index++) {
            PeekingResultIterator iterator = iterators.get(index);
            try {
              iterator.close();
            } catch (Exception e) {
              if (toThrow == null) {
                toThrow = ClientUtil.parseServerException(e);
              } else {
                toThrow.setNextException(ClientUtil.parseServerException(e));
              }
            }
          }
        }
      } catch (Exception e) {
        toThrow = ClientUtil.parseServerException(e);
      } finally {
        setMetricsInParentContext();
        if (toThrow != null) {
          throw toThrow;
        }
      }
    }
  }

  private void setMetricsInParentContext() {
    ReadMetricQueue parentCtxReadMetrics = parentStmtCtx.getReadMetricsQueue();
    for (ReadMetricQueue readMetrics : readMetricsList) {
      parentCtxReadMetrics.combineReadMetrics(readMetrics);
    }
    OverAllQueryMetrics parentCtxQueryMetrics = parentStmtCtx.getOverallQueryMetrics();
    for (OverAllQueryMetrics metric : overAllQueryMetricsList) {
      parentCtxQueryMetrics.combine(metric);
    }
  }

  @Override
  public List<List<Scan>> getScans() {
    if (scans == null) return Collections.emptyList();
    else return scans;
  }

  @Override
  public int size() {
    return scans.size();
  }

  @Override
  public void explain(List<String> planSteps) {
    for (PeekingResultIterator iterator : iterators) {
      iterator.explain(planSteps);
    }
  }

  @Override
  public List<PeekingResultIterator> getIterators() throws SQLException {
    return iterators;
  }

  @Override
  public void explain(List<String> planSteps,
    ExplainPlanAttributesBuilder explainPlanAttributesBuilder) {
    boolean moreThanOneIters = false;
    ExplainPlanAttributesBuilder lhsPointer = null;
    // For more than one iterators, explainPlanAttributes will create
    // chain of objects as lhs and rhs query plans.
    for (PeekingResultIterator iterator : iterators) {
      if (moreThanOneIters) {
        ExplainPlanAttributesBuilder rhsBuilder = new ExplainPlanAttributesBuilder();
        iterator.explain(planSteps, rhsBuilder);
        ExplainPlanAttributes rhsPlans = rhsBuilder.build();
        lhsPointer.setRhsJoinQueryExplainPlan(rhsPlans);
        lhsPointer = rhsBuilder;
      } else {
        iterator.explain(planSteps, explainPlanAttributesBuilder);
        lhsPointer = explainPlanAttributesBuilder;
      }
      moreThanOneIters = true;
    }
  }
}
